1. Field of the Invention
The present invention relates to a camera switchable automatic between and manual exposure control.
2. Description of the Prior Art
In conventional TTL light measuring systems, the brightness of an object is measured by responding to light coming from the object through the camera's objective lens. These systems fall into one of three types, namely an average light measuring system which measures the average intensity of the light passing through the lens, a weighted measuring system which responds mainly to the brightness in the center of the beam from the subject, and a partial light measuring system that measures the brightness only of an important selected portion of the subject.
Each light measuring system has its own advantages and disadvantages. No one can be considered the best. However, various kinds of TTL automatic exposure (AE) control cameras are manufactured. In such cameras, partial photometric systems are not convenient when photographs are taken rapidly. Thus, TTL-AE cameras often use average light measuring or average photometric systems. Such cameras frequently include automatic shutter or aperture controls as well as manual controls and permit free selection of these controls.
In conventional TTL-AE cameras, the exposure is controlled on the basis of the average light measurement even when the camera is operating in the manual mode. However, a photographer may not desire this type of light measuring system in the manual mode.
Moreover, these types of cameras are unable to measure the brightness even when the exposure is mechanically controlled when the voltage of the power source decreases. This makes correct exposure difficult. Normally, the photographer must estimate the needed exposure.
The purpose of the present invention is to eliminate the shortcomings of conventional TTL-AE cameras.
Another purpose of the present invention is to offer an exposure control device so designated that the light measuring circuit is operable with a low voltage even when the circuit does not operate due to the deterioration of the power source apt to take place in the electrically controlled camera in such a manner that all other circuits than the light measuring circuit can be changed over into the mechanical controls.
Further other purposes of the present invention will be disclosed from the explanations to be made below in accordance with embodiments of the present invention.